The present invention relates generally to rotary vane pumps and motors, and more particularly, to stackable rotary vane pumps with improved volumetric efficiency.
Rotary vane pumps and motors are used in many different applications. These devices use mechanical power to compress a fluid when operating as a pump, and can operate as a motor to supply a rotary output when provided with a compressed fluid as a power source. Used as motors, these devices have been used in aircraft in air-assist starting of turbine engines. Also, such devices have been used in aircraft applications as pumps to supply either vacuum or fluid under pressure. To avoid complication of description, these devices will be described herein as pumps, it being understood that the reverse operation as a motor is equally possible.
Typically these pumps comprise a housing including a liner with a bore and a pair of end bearings which support a rotatable shaft. The axis of the liner is parallel to and offset from the axis of the shaft. Vanes slide radially in and out in slots through the shaft and provide pockets which expand and contract with each shaft revolution. The vanes are held in engagement with the bore in the liner by centrifugal force as the shaft rotates.
Axial positioning and sealing of the axial ends of the vanes of prior art pumps has been accomplished in different ways, each with accompanying drawbacks. One technique permits maximum volumetric efficiency but limits design and construction flexibility; another technique has reduced volumetric efficiency but enhanced design flexibility. In this context, volumetric efficiency is increased when the shaft is mounted as nearly tangent to the liner bore as possible. Design flexibility is enhanced when multiple pump units can be mounted on a single shaft.
The first of these prior art techniques is to form shoulders reducing the shaft diameter at opposite ends of the liner. This permits the end bearings of the housing to overlap radially part of the shaft. Thus the end bearings serve to position the vanes axially even where the shaft and liner bore are tangent to each other and the vanes are fully inside the slot in the shaft. However, this design prohibits more than a single pump unit per shaft because the end bearings for each pump unit must be assembled from opposite ends of the shaft.
Another prior art technique for axial positioning of vanes in this type of pump utilizes a shaft of uniform diameter, which permits multiple pump units to be mounted on a single shaft. However, this is accomplished at the expense of reducing volumetric efficiency, in that in order to position the vanes axially when the pockets are at their minimum size, the shaft is mounted short of tangent to the liner bore. Thus the vanes never retract completely and the small amount of the end face of each vane which projects beyond the circumference of the shaft bears against a respective end bearing to position the vane axially. Because the shaft is not tangent to the liner bore and the vanes never retract completely into the shaft, volumetric efficiency is reduced.